DESCRIPTION (Applicant's Abstract): Many studies have revealed distortions in the visual perception of the distance and shape of objects. In view of this, how do people successfully reach to grasp objects? The stability of reaching is also at issue because reaching drifts without haptic feedback from contact with objects. Previously, the investigators have argued that calibration is an essential component of definite distance perception. However, studies of haptic shape perception have also revealed distortions in perceived shape. They will investigate how haptic and visual perception of egocentric distance and shape are combined to allow stable and accurate reaching and grasping. Target spheres will be viewed by participants and then removed by the experimenter before the participant performs blind reaches. Participants will reach to locations at small exocentric distances to the front, back, top, or bottom of a target sphere or reach to location on the surface of the sphere itself. In some conditions, participants will be allowed haptic feedback and in other not. They will investigate stability based on haptic information along and whether vision destabilizes reaching once haptic feedback is removed. They will investigate if the presence of a continuous visible surface facilitates generalization of haptic calibration across reach space. The investigators will examine whether grasping allows greater accuracy and stability than reaching. Finally, they will investigate monocular optic flow generated by head movement. Twenty percent of the general population is estimated to be effectively monocular. The best monocular perception of distance is achieved via optic flow generated by self-motion. They will use head mounted computer graphics displays to rescale the relation between optic flow and self-motion and use the rescaling to investigate the locus and specificity of calibration. This program of research is unique in it attention to both the perceptual and motor side of manual activity and to the inherently multimodal character of spatial behavior. By studying the integrated function of vision and haptics and motor control the investigators hope to generate fundamental understanding of functionally effective spatial behaviors.